合并2个列表并删除重复项.在第三个列表中输出.我的尝试不起作用

Question

当我需要比较2个列表并生成包含所有唯一项目的第3个列表时,我似乎总是遇到问题.我需要经常执行此操作.

尝试用一个简单的例子重现这个问题.

我错过了什么吗？谢谢你的任何建议

想要的结果

   Name= Jo1 Surname= Bloggs1 Category= Account
   Name= Jo2 Surname= Bloggs2 Category= Sales
   Name= Jo5 Surname= Bloggs5 Category= Development
   Name= Jo6 Surname= Bloggs6 Category= Management
   Name= Jo8 Surname= Bloggs8 Category= HR
   Name= Jo7 Surname= Bloggs7 Category= Cleaning

class Program
{
    static void Main(string[] args)
    {
          List<Customer> listOne = new List<Customer>();
        List<Customer> listTwo = new List<Customer>();

        listOne.Add(new Customer { Category = "Account", Name = "Jo1", Surname = "Bloggs1" });
        listOne.Add(new Customer { Category = "Sales", Name = "Jo2", Surname = "Bloggs2" });
        listOne.Add(new Customer { Category = "Development", Name = "Jo5", Surname = "Bloggs5" });
        listOne.Add(new Customer { Category = "Management", Name = "Jo6", Surname = "Bloggs6" });



        listTwo.Add(new Customer { Category = "HR", Name = "Jo8", Surname = "Bloggs8" });
        listTwo.Add(new Customer { Category = "Sales", Name = "Jo2", Surname = "Bloggs2" });
        listTwo.Add(new Customer { Category = "Management", Name = "Jo6", Surname = "Bloggs6" });
        listTwo.Add(new Customer { Category = "Development", Name = "Jo5", Surname = "Bloggs5" });
        listTwo.Add(new Customer { Category = "Cleaning", Name = "Jo7", Surname = "Bloggs7" });


    List<Customer> resultList = listOne.Union(listTwo).ToList();//**I get duplicates why????**

        resultList.ForEach(customer => Console.WriteLine("Name= {0} Surname= {1} Category= {2}", customer.Name, customer.Surname, customer.Category));
        Console.Read();

        IEnumerable<Customer> resultList3 = listOne.Except(listTwo);//**Does not work**

        foreach (var customer in resultList3)
        {
            Console.WriteLine("Name= {0} Surname= {1} Category= {2}", customer.Name, customer.Surname, customer.Category);
        }

        **//Does not work**
        var resultList2 = (listOne
                       .Where(n => !(listTwo
                           .Select(o => o.Category))
                           .Contains(n.Category)))
                       .OrderBy(n => n.Category);

        foreach (var customer in resultList2)
        {
            Console.WriteLine("Name= {0} 
                             Surname= {1} 
                             Category= {2}", 

customer.Name,customer.Surname,customer.Category); Console.Read();

  }
}

public class Customer
{
    public string Name { get; set; }
    public string Surname { get; set; }
    public string Category { get; set; }
}

Answer 1

难道你不能通过使用Concat和DistinctLINQ方法吗？

List<Customer> listOne;
List<Customer> listTwo;

List<Customer> uniqueList = listOne.Concat(listTwo).Distinct().ToList(); 

如有必要,可以使用带有IEqualityComparer的Distinct()重载来创建自定义相等比较

Answer 2

The crux of the problem is the Customer object doesn't have a .Equals() implementation. If you override .Equals (and .GetHashCode) then .Distinct would use it to eliminate duplicates. If you don't own the Customer implementation, however, adding .Equals may not be an option.

An alternative is to pass a custom IEqualityComparer to .Distinct(). This lets you compare objects in different ways depending on which comparer you pass in.

Another alternative is to GroupBy the fields that are important and take any item from the group (since the GroupBy acts as .Equals in this case). This requires the least code to be written.

e.g.

    var result = listOne.Concat(listTwo)
        .GroupBy(x=>x.Category+"|"+x.Name+"|"+x.Surname)
        .Select(x=>x.First());

which gets your desired result.